Many semiconductor processes are typically performed in a vacuum environment, i.e., a sealed chamber containing an assembly for supporting the wafer substrate(s) disposed therein. In a semiconductor process, a heating apparatus typically includes a ceramic support that may have electrodes disposed therein to heat the support, and additionally may have electrodes that electrostatically hold the wafer or substrate against the ceramic support, i.e., electrostatic chuck or ESC (also sometimes called susceptors). A semiconductor device fabrication process can take place in the chamber, including deposition, etching, implantation, oxidation, etc. As an example of a deposition process one can conceive of a physical vapor deposition (PVD) process, known as sputter deposition, in which a target generally comprised of a material to be deposited on the wafer substrate is supported above the substrate, typically fastened to a top of the chamber. Plasma is formed from a gas such as argon supplied between the substrate and the target. The target is biased causing ions within the plasma to be accelerated toward the target. The ions of the plasma interact with the target material, and cause atoms of the material to be sputtered off, travel through the chamber toward the wafer, and redeposit on the surface of a semiconductor wafer that is being processed into integrated circuits (IC's). Other deposition processes may include, but are not limited to, plasma enhanced chemical vapor deposition (PECVD), high density plasma chemical vapor deposition (HDP-CVD), low pressure chemical vapor deposition (LPCVD), sub-atmospheric pressure chemical vapor deposition (SACVD), metal organic chemical vapor deposition (MOCVD), molecular beam evaporation (MBE), etc.
In some of the above processes it is desirable to heat the wafer by heating the support. The chemical reaction rate of the materials being deposited, etched, implanted, etc, is controlled to some degree by the temperature of the wafer. Undesirable unevenness in deposition, etching, implantation, etc., over a face of the wafer can easily result if the temperature of the wafer across its area varies too much. In most cases, it is highly desirable that deposition, etching, implantation be uniform to a nearly perfect degree since otherwise the IC's being fabricated at various locations on the wafer will have electronic characteristics that deviate from the norm more than is desirable.
Molded aspheric lenses are commonly used in consumer cameras, camera phones, and CD players due to their low cost and good performance. They are also commonly used for laser diode collimation, and for coupling light into and out of optical fibers. In molding a glass mass to make an aspheric lens, a pair of metal or ceramic molds are used. In this process, a plurality of heaters are used to heat up the molds until the glass mass is softened with the temperature of the glass mass can reach up to 600° C. As with a semiconductor-processing chamber, it is desirable that the molds be uniformly heated and their temperatures be closely controlled.
Various attempts have been tried to control the temperature of a substrate such as a wafer or molded lenses in the prior art. In one example of semiconductor process, an inert coolant gas (such as helium or argon) is admitted at a single pressure within a single thin space between the bottom of the wafer and the top of the ESC which holds the wafer. This approach is referred to as backside gas cooling. Another prior art way of dealing with the need for zone cooling, i.e., uniform temperature control is to vary the surface roughness or to cut a relief pattern to effectively change the local contact area. Yet another way of dealing with the need for zone cooling is to use coolant gas whose pressure is varied to increase and fine-tune thermal transport.
US Patent Publication No. 2006/0144516A1 controls the temperature of a substrate by the use of adhesive materials, i.e., a first layer of adhesive material to bond the metal plate and the heater to the top surface of the temperature controlled base, and a second layer of adhesive material bonds the layer of dielectric material to a top surface of the metal plate. The adhesive possesses physical properties that allow the thermal pattern to be maintained under varying external process conditions.
There still exists a need for a heating apparatus providing relatively uniform temperature distribution to a substrate and a method for controlling the temperature of the substrate placed thereon, during processing of a wafer in semiconductor device fabrication and for other substrates in similar processes.